Pisa's origins remained unknown for centuries. The city lies at the junction of two rivers, the Arno and the Serchio in the Ligurian Sea forming a laguna area. The Pelasgi, the Greeks, the Etruscans and the Ligurians have variously been proposed as founders of the city. Archeological remains from the 5th century BC confirmed the existence of a city at the sea, trading with Greeks and Gauls. The presence of an Etruscan necropolis, discovered during excavations in the Arena Garibaldi in 1991, allowed to clarify its Etruscan origins.

Ancient Roman authors referred to Pisa as an old city. Servius wrote that the Teuti, or Pelopes, the king of the Pisei, founded the town thirteen centuries before the start of the common era. Strabo referred Pisa's origins to the mythical Nestor, king of Pylos, after the fall of Troy. Virgil in his Aeneid states that Pisa was already a great and developed centre by the times described; the foundation of the city in the 'Etruscan lands' has been credited to settlers from the Alpheus coast.